This invention involves antennas and relates to measurements of electromagnetic wave field characterizations. Specifically, it relates to a method and a system dealing with determination of wave polarization and direction of wave propagation for arbitrary frequencies.
Many man-made electronic applications generate radio-frequency waves. Within the radio frequency spectrum there are nowadays numerous sources, both man-made and naturally occurring. The man-made sources may be intentional, for example normal communication systems, or they may be unintentional, for example electromagnetic contamination (EMC). Often the exact position of the source is not known and in such cases it would be of great value to know the direction to the source and thereby also be able to estimate the position of the source.
In the past several techniques have been deployed to identify the location of the source. Methods like xe2x80x9chigh-gainxe2x80x9d antenna bearing, interferometry with two or more receivers separated by a distance that scales with the wavelength, and triangulation are in use today.
The present invention utilizes the polarization properties of electromagnetic fields to determine the direction to the source. Furthermore the measurements need not be from more than one point in space. In this respect a one-point measurement is considered to be such that all antennas are well within a sphere of a wavelength scale.
Assuming separate frequencies, the present invention also makes it possible to distinguish between several sources and register their separate polarization simultaneously. At least three electric antennas, or three magnetic antennas, are used to measure the wave field. The antennas are arranged such that three spatial components of the wave field can be registered. The registered field components need not be a priori orthogonal to each other. The measured wave field is processed in accordance to predetermined formulae so that the propagation direction and other polarization characteristics, such as the spectral intensity and the spectral degree of circular polarization, are derived.
The present invention is set forth by the independent claims 1 and 6 and different embodiments are set forth by the dependent claims 2-5 and 7-10.